This invention relates to a method of, and an apparatus for marking center lines, lane lines, etc., on roadways. More particularly, it is directed to marking road surfaces with a melted thermoplastic material, and preferably a thermoplastic material containing reflective glass beads.
It has become conventional practice to spray a marking material onto a road surface to mark traffic center lines, lane lines, etc. The marking material for forming these lines generally is either a rapidly curing paint or a thermoplastic resinous material. Preferably reflective beads are included in the marking materials.
More recently thermoplastic marking materials have gained in importance in marking road surfaces due to the ability to apply a thicker and, therefore, longer lasting line. Although line marking apparatus for applying a thermoplastic material which include means for heating the thermoplastic material to a liquid melt and means for spraying the melted thermoplastic material onto the pavement are known, none is fully satisfactory from the standpoint of temperature control, compactness, and convenience. Moreover, in instances where reflective beads are included in the line, it has been the practice to premix the beads and thermoplastic, and spray the melted premix.
Specifically, U.S. Pat. No. 3,664,242 to Harrington et al, issued May 23, 1972, discloses a method of forming a marking on a roadway in which the roadway is heated to a temperature of about 150.degree. F., to 500.degree. F., and a marking material comprising a continuous stream of solid individual particles of a coloring agent and a resinous material is projected onto the heated area. The individual particles are heated, as they proceed toward the roadway, to a temperature sufficient to soften a major portion of the thermoplastic phase before the particles reach the pavement. U.S. Pat. No. 3,477,352 to Harding et al, issued Nov. 11, 1969, describes a self-propelled apparatus for applying markings to a roadway in which a strip of thermoplastic road marking material is sprayed onto the road surface. Depending upon weather conditions the road surface can be first sprayed with an adhesive material. An additional spray gun sprays a reflective marking material onto the strip of thermoplastic material before it cools and sets. U.S. Pat. No. 3,682,054 to MacPhail et al, issued Aug. 8, 1972, describes an apparatus mounted on a truck for applying a two-component epoxy resin marking composition to a roadway. The truck body is a closed, heat-insulated chamber. Separately heated supply vessels are provided for the resin and the curing agent. A cart, which moves along behind the truck, sprays the two components onto the surface to be marked. U.S. Pat. No. 3,554,449 to Currie, issued Jan. 12, 1971, discloses a portable plastic melter for melting large amounts of thermoplastic material containing glass beads or other aggregate. U.S. Pat. No. 3,286,605 to Wilson et al, issued Nov. 22, 1966, describes an apparatus for marking road surfaces whereby a spray line of marking material is applied to the surface and a stream of glass beads is applied to the spray line while the marking material is still wet. An essential feature of the Wilson et al method is in the size of the glass spheres, whereby the heavier spheres are imbedded in the spray and the lighter spheres become deposited on top of the wet spray line to provide an immediately reflective surface.